Method for hydrotreatment of a heavy hydrocarbon fraction with switchable reactors and reactors capable of being shorted out

ABSTRACT

The invention consists in a process for hydrotreating a heavy hydrocarbon fraction in a first hydrodemetallisation section, then in a second hydrodesulphurisation section into which the effluent from the first section is passed. The hydrodemetallisation section is preceded by at least one guard zone. Said hydrotreatment process comprises the following steps:  
     a) a step in which the guard zone is used;  
     b) a step during which the guard zone is short-circuited and the catalyst it contains is regenerated and/or replaced;  
     c) a step during which the guard zone in which the catalyst has been regenerated and/or replaced is reconnected;  
     d) a step in which at least one of the reactors from the hydrodemetallisation section and/or the hydrodesulphurisation section can be short-circuited and the catalyst it contains regenerated and/or replaced.

[0001] The present invention relates to refining and converting heavyhydrocarbon fractions containing, inter alia, sulphur-containing andmetallic impurities, such as atmospheric residues, vacuum residues,deasphalted oils, pitches, asphalts mixed with an aromatic distillate,coal hydrogenates, heavy oils of any origin and in particular those frombituminous schists or sands. In particular, it relates to treatingliquid feeds. The scope of the invention also encompasses asphaltenesalso being contained in the liquid feed.

[0002] Feeds which can be treated in accordance with the inventionnormally comprise at least 0.5 ppm by weight of metals (nickel and/orvanadium) and at least 0.5% by weight of sulphur.

[0003] The aim of catalytic hydrotreatment of such feeds is both torefine, i.e., to substantially reduce their metal, sulphur and otherimpurity contents while increasing the hydrogen-to-carbon ratio (H/C)while transforming them to a greater or lesser extent to lighter cuts,the different effluents obtained possibly serving as bases for theproduction of high quality fuel, gas oil and gasoline, or feeds forother units such as residue cracking or cracking vacuum distillates.

[0004] The problem with catalytic hydrotreatment of such feedsoriginates from the fact that such impurities gradually depositthemselves on the catalyst in the form of metals and coke, and tend torapidly deactivate and clog the catalytic system, which necessitates astoppage to replace it.

[0005] Processes for hydrotreating that type of feed must therefore bedesigned to allow as long as possible a cycle of operation withoutstopping the unit, the aim being to attain a minimum one year cycle ofoperation.

[0006] A variety of treatments for this type of feed exist. Suchtreatments have until now been carried out:

[0007] either in processes using fixed catalyst beds (for example theHYVAHL-F process from the Institut Francais du Pétrole);

[0008] or in processes comprising at least one reactor enabling thecatalyst to be replaced quasi-continuously (for example the HYVAHL-Mmoving bed process from the Institut Francais du Pétrole).

[0009] The process of the present invention is an improvement over priorart processes, in particular fixed or ebullated bed processes. In suchprocesses, the feed circulates through a plurality of reactors,preferably fixed or ebullated bed reactors, disposed in series, thefirst reactor or reactors being used to carry out hydrodemetallisation(HDM) of the feed in particular and part of the hydrodesulphurisation,the final reactor or reactors being used to carry out deep refining ofthe feed, and in particular hydrodesulphurisation (HDS step). Theeffluents are withdrawn from the last HDS reactor.

[0010] In such processes, specific catalysts adapted to each step areusually used, under average operating conditions of about 5 MPa to about25 MPa, preferably about 10 MPa to about 20 MPa, and a temperature ofabout 370° C. to 420° C.

[0011] For the HDM step, the ideal catalyst must be suitable fortreating feeds which are rich in asphaltenes, while having a highdemetallisation capacity associated with a high metal retention capacityand a high resistance to coking. The Applicant has developed such acatalyst on a particular macroporous support (the “sea urchin”structure) which endows it with precisely the desired qualities for thisstep (European patents EP-B-0 113 297 and EP-B-0 113 284):

[0012] a degree of demetallisation of at least 10% to 90% in the HDMstep;

[0013] a metal retention capacity of more than 10% with respect to theweight of new catalyst, which results in longer cycles of operation;

[0014] high resistance to coking even at temperatures of more than 390°C. which contributes to extending the cycle period which is oftenlimited by increasing the pressure drop and the activity loss due tocoke production, and which means that the majority of the thermalconversion can be carried out in this step.

[0015] For the HDS step, the ideal catalyst must have a highhydrogenating power so as to carry out deep refining of the products:desulphurisation, continuation of demetallisation, reducing theConradson carbon and possibly the amount of asphaltenes. The Applicanthas developed such a catalyst (EP-B-0 113 297 and EP-B-0 113 284) whichis particularly suitable for treating that type of feed.

[0016] The disadvantage of that type of high hydrogenating capacitycatalyst is that it rapidly deactivates in the presence of metals orcoke. For this reason, combining a suitable HDM catalyst, which canfunction at a relatively high temperature to carry out most of theconversion and demetallisation, with a suitable HDS catalyst, which canbe operated at a relatively low temperatures as it is protected frommetals and other impurities by the HDM catalyst which encourages deephydrogenation and limits coking, then in the end overall refiningperformances are obtained which are higher than those obtained with asingle catalytic system or with those obtained with a similar HDM/HDSarrangement using an increasing temperature profile which leads to rapidcoking of the HDS catalyst.

[0017] The importance of fixed bed processes is that high refiningperformances are obtained because of the high catalytic efficacy offixed beds. In contrast, above a certain quantity of metals in the feed(for example 50 to 150 ppm), even though better catalytic systems areused, the performances and especially the operating period for suchprocesses becomes insufficient: the reactors (in particular the firstHDM reactor) rapidly become charged with metals and thus deactivate; tocompensate for that deactivation, the temperatures are increased, whichencourages coke formation and increases pressure drops; further, it isknown that the first catalytic bed is susceptible to becoming cloggedquite rapidly because of the asphaltenes and sediments contained in thefeed or as a result of operating problems.

[0018] The result is that the unit has to be stopped a minimum of every2 to 6 months to replace the first deactivated or clogged catalyticbeds, that operation possibly lasting up to three weeks and furtherreducing the service factor of the unit.

[0019] The importance of ebullated bed processes is that the conversionperformance is high due to the possibility of working at hightemperatures. The Applicant has developed a process that is eminentlysuitable for treating conventional and heavy feeds (Canadian patent CA-2171 894, French patent application FR-98/00530).

[0020] Although the best catalytic systems are used, the operation timecan be reduced during problems in operations and/or during use notsuited to the feed. The unit is thus stopped depending on how much cokeis present in the reactor. We have attempted to solve these problems ofoperation and use of the catalyst.

[0021] We have also sought to overcome the disadvantages of fixed bedarrangements in different manners.

[0022] Thus, one or more moving bed reactors have been proposed,installed at the head of the HDM step (United States patents U.S. Pat.No. 3,910,834 or British patent GB-B-2 124 252). Such moving beds canoperate in co-current mode (the HYCON process from SHELL, for example)or in counter-current mode (the Applicant's HYVAHL-M process, forexample). This protects the reactors, for example fixed bed reactors bycarrying out part of the demetallisation and filtering the particlescontained in the feed which could lead to clogging. Further,quasi-continuous replacement of the catalyst in that or those moving bedreactors avoids the need to stop the unit every 3 to 6 months.

[0023] The disadvantage of such moving bed techniques is that overall,their performances and efficiency are rather inferior to those for fixedbeds of the same size, that they cause attrition of the circulatingcatalyst which can lead to obstruction of the fixed beds locateddownstream, and which above all, under the operating conditions used,the risks of coking and thus the formation of agglomerates of catalystare far from negligible with such heavy feeds, in particular in theevent of problems. These agglomerates can prevent the catalyst fromcirculating either in the reactor or in the used catalyst withdrawallines, and finally cause stoppage of the unit to clean the reactor andthe withdrawal lines.

[0024] In order to retain excellent performance while maintaining anacceptable service factor, the addition of a guard reactor, preferably afixed bed reactor (space velocity HSV=2 to 4) in front of the HDMreactors has been considered (U.S. Pat. No. 4,118,310 and U.S. Pat. No.3,968,026). Usually, this guard reactor can be short-circuited by usingan isolation valve in particular. Thus the principal reactors aretemporarily protected against clogging. When the guard reactor isclogged it is short-circuited, but then the following principal reactorcan become clogged in its turn and lead to stoppage of the unit.Further, the small size of the guard reactor does not ensure a highdegree of demetallisation of the feed and thus is a poor protector ofthe principal HDM reactors against the deposition of metals in the caseof metal-rich feeds (more than 100 ppm, for example). Thus thosereactors undergo accelerated deactivation leading to too frequentstoppages of the unit and thus to service factors which are stillinsufficient.

[0025] FR-B1-2 681 871 describes a system that combines good fixed bedperformance with a high service factor for the treatment of feeds with ahigh metal content (1 to 1500 ppm but usually 100 to 1000 and preferably150 to 350 ppm) which consists in a hydrotreatment process carried outin at least two steps to hydrotreat a heavy hydrocarbon fractioncontaining sulphur-containing impurities and metallic impurities inwhich in a first section, hydrodemetallisation, the hydrocarbon feed andhydrogen are passed over a hydrodemetallisation catalyst underhydrodemetallisation conditions then in a subsequent second step, theeffluent from the first section is passed over a hydrodesulphurisationcatalyst under hydrodesulphurisation conditions. In this process, thehydrodemetallisation section comprises one or more hydrodemetallisationzones, preferably with fixed beds, preceded by at least twohydrodemetallisation guard zones, also preferably with fixed beds,disposed in series for cyclic use consisting of successive repetition ofsteps b) and c) defined below:

[0026] a) a step in which the guard zones are used together for a periodat most equal to the deactivation time and/or clogging time for onethereof;

[0027] b) a step during which the deactivated and/or clogged guard zoneis short-circuited and the catalyst it contains is regenerated and/orreplaced by fresh catalyst; and

[0028] c) a step during which the guard zones are all used together, theguard zone where the catalyst has been regenerated during the precedingstep being reconnected and said step being carried out for a period atmost equal to the deactivation and/or clogging time for one of the guardzones.

[0029] This process produces a cycle period which is in general at least11 months for the principal HDM and HDS reactors with high performancesfor refining and conversion while retaining the stability of theproducts. The overall desulphurisation is of the order of 90% and theoverall demetallisation is of the order of 95%.

[0030] The disadvantage of this technology is the difficulty ofobtaining overall desulphurisation performances of more than about 90%and/or overall demetallisation performances of more than about 95%, andthe difficulty of obtaining cycle times of more than 11 monthsindependent of performance levels. It has surprisingly been discoveredthat short-circuiting one or more reactors of the hydrodemetallisationand/or hydrodesulphurisation section can maintain the catalytic activityfor each of the steps and/or improve the cycle time.

[0031] The present invention concerns the possibility ofshort-circuiting one or more reactors when the catalyst is deactivatedand/or clogged by sediments or coke to be regenerated and/or replaced byfresh or regenerated catalyst. This invention concerns both reactorsfrom the hydrodemetallisation section and reactors from thehydrodesulphurisation section.

[0032] It follows that the reactors from the hydrodemetallisationsection and/or hydrodesulphurisation section are, for example,short-circuited every 6 months to replace the deactivated or cloggedcatalytic beds; this operation improves the service factor of the unit.

[0033] The invention consists in a process for hydrotreating a heavyhydrocarbon fraction in a first hydrodemetallisation section, then in asecond hydrodesulphurisation section into which the effluent from thefirst section is passed. The hydrodemetallisation section is preceded byat least one guard zone. Said hydrotreatment process comprises thefollowing steps:

[0034] a) a step in which the guard zone is used;

[0035] b) a step during which the guard zone is short-circuited and thecatalyst it contains is regenerated and/or replaced;

[0036] c) a step during which the guard zone in which the catalyst hasbeen regenerated and/or replaced is reconnected;

[0037] d) a step in which at least one of the reactors from thehydrodemetallisation section and/or the hydrodesulphurisation sectioncan be short-circuited and the catalyst it contains regenerated and/orreplaced.

[0038] A route for improving fixed bed performance, summarised below,has also been described by the Applicant in FR-A-2 784 687. That conceptcan also be applied to the present invention.

[0039] However, there is some difficulty associated with the highviscosity of the feed and the total liquid effluent which causes highpressure drops in the reactor and difficulties in the operation of therecycling compressor, often resulting in a rather low hydrogen pressurewhich does not encourage either good hydrodemetallisation or goodhydrodesulphurisation. Further, it has been shown that the gas oilfraction obtained normally cannot directly be used as its sulphurcontent is higher than current specifications allow.

[0040] It is desirable and possible to improve the performance of aprocess such as that described by the Applicant in French patentsFR-B1-2 681 871 and FR-A-2 784 687. In particular, the process of thepresent invention can very substantially reduce the viscosity of theliquid effluents, resulting in a substantial reduction in the pressuredrops in the reactors, better operation of the recycling compressor andthe production of a higher hydrogen pressure. This results in higheroverall desulphurisation and a gas oil fraction with a much lowersulphur content, satisfying the current specifications and which can bedirectly used in the gas oil pool of the refinery. Further, in theprocess of the present invention, the preheat furnaces function betterbecause of better heat transfer and thus the skin temperature of thesefurnaces is lower which helps to increase the service life of thefurnaces and thus contributes to reducing the operating costs of theunit.

[0041] The process of the invention, which combines high performances ofthe reactors, preferably fixed bed reactors or ebullated bed reactors,with a high service factor for treating feeds with high metal contents(1 to 1500 ppm, but usually 100 to 1000 and preferably 150 to 350 ppm)can be defined in one of its variations as a process for hydrotreating,in at least two sections, a heavy hydrocarbon fraction containingsulphur-containing and metallic impurities in which, in a first,hydrodemetallisation, section, the hydrocarbon feed and hydrogen arepassed over a hydrodemetallisation catalyst under hydrodemetallisationconditions, then the effluent from the first section is passed over ahydrodesulphurisation catalyst in a subsequent second section underhydrodesulphurisation conditions, and in which the hydrodemetallisationsection comprises one or more hydrodemetallisation zones, preferablyfixed bed or ebullated bed zones, preceded by at least one or possiblytwo hydrodemetallisation guard zones, also preferably fixed bed orebullated bed zones, disposed in series for use in a cycle consisting ofsuccessive repetitions of steps b) and c) defined below, thehydrodemetallisation and/or hydrodesulphurisation sections beingcomposed of one or more reactors, preferably fixed bed or ebullated bedreactors, which can be short-circuited separately or otherwise followingstep d) defined below. When two guard zones are used, the process of theinvention is a hydrotreatment process comprising:

[0042] a) a step in which the guard zones are used all together for aperiod at most equal to the deactivation time and/or clogging time ofone thereof;

[0043] b) a step during which the deactivated and/or clogged guard zoneis short-circuited and the catalyst it contains is regenerated and/orreplaced by fresh or regenerated catalyst;

[0044] c) a step during which the guard zones are used all together, theguard zone in which the catalyst has been regenerated and/or replacedduring the preceding step being reconnected and said step being carriedout for a period at most equal to the deactivation and/or clogging timeof one of the guard zones;

[0045] d) a step in which at least one of the reactors from thehydrodemetallisation section and/or the hydrodesulphurisation sectioncan be short-circuited during a cycle when the catalyst is deactivatedand/or clogged for regeneration and/or replacement by fresh orregenerated catalyst.

[0046] A further variation of the process of the invention consists in aprocess for hydrotreating, in at least two sections, a heavy hydrocarbonfraction containing sulphur-containing and metallic impurities, in whichin a first hydrodemetallisation, section, the hydrocarbon feed andhydrogen are passed over a hydrodemetallisation catalyst underhydrodemetallisation conditions, then the effluent from the first stepis passed over a hydrodesulphurisation catalyst in a subsequent secondsection under hydrodesulphurisation conditions, and in which thehydrodemetallisation section comprises one or more hydrodemetallisationzones preceded by at least one hydrodemetallisation guard zone, thehydrodemetallisation and/or hydrodesulphurisation sections beingcomposed of one or more reactors which can be short-circuited separatelyor otherwise following step d) defined below, said hydrotreatmentprocess comprising:

[0047] a) a step in which the guard zone is used for a period at mostequal to the deactivation time and/or clogging time of said zone;

[0048] b) a step during which the deactivated and/or clogged guard zoneis short-circuited and the catalyst it contains is regenerated and/orreplaced by fresh or regenerated catalyst;

[0049] c) a step during which the guard zone in which the catalyst hasbeen regenerated and/or replaced during the preceding step isreconnected, said step being carried out for a period at most equal tothe deactivation and/or clogging time of one of the guard zones;

[0050] d) a step in which at least one of the reactors from thehydrodemetallisation section and/or the hydrodesulphurisation sectioncan be short-circuited during a cycle when the catalyst is deactivatedand/or clogged for regeneration and/or replacement by fresh orregenerated catalyst.

[0051] In a variation of the process of the invention, the feed for saidprocess is a heavy hydrocarbon fraction containing sulphur-containingand metallic impurities, in general at least 0.5 ppm by weight ofmetals, for example a fraction obtained by vacuum distillation, termed avacuum distillate (VD).

[0052] Preferably, in the process of the invention, a quantity of middledistillate generally representing about 0.5% to about 80% by weight withrespect to the weight of hydrocarbon feed is introduced into the firstfunctioning guard zone.

[0053] More preferably, the quantity of middle distillate introducedrepresents about 1% to about 50%, by weight, highly preferably about 5%to about 25% by weight with respect to the weight of hydrocarbon feed.

[0054] In a particular implementation, the atmospheric distillate whichis introduced with the hydrocarbon feed is a straight run gas oil.

[0055] In a further implementation, the product from thehydrodesulphurisation step is sent to an atmospheric distillation zonefrom which an atmospheric distillate is recovered at least a portion ofwhich is recycled to the inlet to the first functioning guard zone, andan atmospheric residue is recovered.

[0056] In a particular variation, at least a portion of a gas oilfraction from the atmospheric distillation is recycled. In this case,the gas oil cut which is recycled is usually a cut with an initialboiling point of about 140° C. and with an end point of about 400° C.Usually this cut is a 150-370° C. cut, or a 170-350° C. cut.

[0057] In a further possible variation of the process of the invention,a gas oil from a unit functioning using the HYVAHL process can berecycled, or a light gas oil from a catalytic cracking unit, usuallyknown as an LCO (light cycle oil) with an initial boiling pointgenerally in the range about 140° C. to about 220° C. and an end pointgenerally in the range about 340° C. to about 400° C. It is alsopossible to recycle a fraction of heavy gas oil from catalytic cracking,usually termed an HCO (high cycle oil) with an initial boiling point inthe range about 340° C. to about 380° C. and with a final boiling pointgenerally in the range about 350° C. to about 550° C.

[0058] The quantity of atmospheric distillate and/or gas oil which isrecycled represents about 1% to 50%, preferably 5% to 25%, morepreferably about 10% to 20% by weight, with respect to the feed.

[0059] In a further variation, at least a portion of the atmosphericresidue from the atmospheric distillation zone is sent to a vacuumdistillation zone from which a vacuum distillate is recovered at least aportion of which is recycled to the inlet to the first functioning guardzone, and a vacuum residue is also recovered which can be sent to therefinery fuel pool.

[0060] In a further variation, at least a portion of the atmosphericresidue and/or vacuum distillate is sent to a catalytic cracking unit,preferably a fluidised bed catalytic cracking unit, for example a unitsuch as that using the R2R process developed by the Applicant. From thiscatalytic cracking unit, an LCO fraction and an HCO fraction inparticular are recovered at least part of either one or the other, or amixture of the two, can be added to the fresh feed which is sent to thehydrotreatment process of the present invention. Usually, a gas oilfraction, a gasoline fraction and a gaseous fraction are also recovered.At least a portion of this gas oil fraction can optionally be recycledto the inlet to the first functioning guard zone.

[0061] The catalytic cracking step can be carried out in a conventionalmanner known to skilled persons under suitable residue crackingconditions to produce hydrocarbon-containing products with a lowermolecular weight. Descriptions of the operation and catalysts which canbe used in fluidised bed cracking can be found, for example, in U.S.Pat. No. 4,695,370, EP-B-0 184 517, U.S. Pat. No. 4,959,334, EP-B-0 323297, U.S. Pat. No. 4,965,232, U.S. Pat. No. 5,120,691, U.S. Pat. No.5,344,544, U.S. Pat. No. 5,449,496, EP-A-0 485 259, U.S. Pat. No.5,286,690, U.S. Pat. No. 5,324,696 and EP-A-0 699 224 the descriptionsof which are hereby incorporated into the present description by dint oftheir mention.

[0062] The fluidised bed catalytic cracking reactor can function inupflow or downflow mode. While this is not a preferred embodiment of theinvention, it is also possible to carry out catalytic cracking in amoving bed reactor. Particularly preferred catalytic cracking catalystsare those which contain at least one zeolite usually mixed with anappropriate matrix such as alumina, silica or silica-alumina.

[0063] The process of the invention includes a particular variation inwhich during step c) the guard zones are used all together, the guardzone where the catalyst has been regenerated during step b) beingreconnected such that its connection is identical to that which it hadbefore it was short-circuited during step b).

[0064] The process of the invention comprises a further variation, whichconstitutes a preferred implementation of the present invention,comprising the following steps:

[0065] a) a step in which the guard zones are all used together for aperiod at most equal to the deactivation and/or clogging time of theguard zone the most upstream with respect to the overall direction ofcirculation of the treated feed;

[0066] b) a step during which the feed penetrates directly into theguard zone located immediately after that which was the most upstreamduring the preceding step and during which the guard zone which was themost upstream during the preceding step is short-circuited and thecatalyst which it contains is regenerated and/or replaced by fresh orregenerated catalyst; and

[0067] c) a step during which the guard zones are used all together, theguard zone in which the catalyst has been regenerated and/or replacedduring the preceding step being reconnected so as to be downstream ofthe set of guard zones and said step being continued for a period atmost equal to the deactivation and/or clogging time of the guard zonewhich during this step is the most upstream with respect to the overalldirection of circulation of the treated feed;

[0068] d) a step in which at least one of the reactors from thehydrodemetallisation section and/or hydrodesulphurisation section can beshort-circuited during the cycle when the catalyst is deactivated and/orclogged to be regenerated and/or replaced by fresh or regeneratedcatalyst.

[0069] In the preferred implementation of the process, the guard zonewhich is the most upstream in the overall direction of circulation ofthe feed gradually becomes charged with metals, coke, sediments and avariety of other impurities and is disconnected when desired but usuallywhen the catalyst it contains is practically saturated with metals andvarious impurities.

[0070] In a preferred implementation, a particular conditioning sectionis used which permits permutation of these guard zones during operation,i.e., without stopping the unit's operation: firstly, a system whichoperates under moderate pressure (1 to 5 MPa but preferably 1.5 to 2.5MPa) carries out the following operations on the disconnected guardreactor: washing, stripping, cooling, before discharging the usedcatalyst; then heating and sulphurisation after charging with freshcatalyst; then a further pressurisation/depressurisation and tap/valvesystem using appropriate technology effectively interchanges these guardzones without stopping the unit, i.e., without affecting the servicefactor, since all of the washing, stripping, discharging of usedcatalyst, recharging of fresh catalyst, heating and sulphurisationoperations are carried out on the disconnected reactor or guard zone.

[0071] The reactors of the hydrotreatment unit usually function with thefollowing hourly space velocities (HSV): HSV (h⁻¹) HSV (h⁻¹) Broad rangePreferred range Total HDM step: (including 0.2-4.0 0.3-0.4 guardreactors) Total HDS step: 0.2-4.0 0.25-0.4  Overall (HDM + HDS):0.10-2.0  0.12-0.30

[0072] The preferred mode consists of operating the guard reactors orzones in service at an overall HSV of about 0.1 to 4.0 h⁻¹, usuallyabout 0.2 to 1.0 h⁻¹, which differs from other processes using smallerguard reactors, in particular as described in U.S. Pat. No. 3,968,026where smaller guard reactors are used. The value of the HSV of eachfunctioning guard reactor is preferably about 0.5 to 8 h⁻¹ and usuallyabout 1 to 2 h⁻¹. The overall HSV of the guard reactors and that of eachreactor is selected so as to carry out maximum hydrodemetallisation(HDM) while controlling the reaction temperature (limiting theexothermicity).

[0073] In an advantageous implementation, the unit comprises aconditioning section, not shown in the Figures, provided withcirculation means, heating means, cooling means and suitable separationmeans functioning independently of the reaction section, whereby withthe aid of lines and valves, the operations of preparing fresh orregenerated catalyst contained in the guard reactor and for theshort-circuited reactor just before being connected, with the unit inoperation, can be carried out, namely: pre-heating the guard reactorduring permutation or short-circuiting, sulphurising the catalyst itcontains, and bringing it to the required pressure and temperatureconditions. When the permutation or short-circuiting operation of thisguard reactor has been carried out using a set of suitable valves, thissame section can also carry out the operations of conditioning the usedcatalyst contained in the guard reactor just after disconnection of thereaction section, namely: washing and stripping the used catalyst underthe required conditions, then cooling before proceeding to theoperations of discharging this used catalyst then replacing it withfresh or regenerated catalyst.

[0074] Preferably again, these catalysts are those described in theApplicant's patents EP-B-0 098 764 and the French patent filed withnational registration number 97/07149. They contain a support and 0.1%to 30% by weight, expressed as the metal oxides, of at least one metalor compound of a metal of at least one of groups V, VI and VHI of theperiodic table and in the form of a plurality of juxtaposed agglomerateseach formed from a plurality of acicular platelets, the platelets ofeach agglomerate generally being radially orientated with respect toeach other and with respect to the centre of the agglomerate.

[0075] More particularly, the present patent application concerns thetreatment of heavy petroleum or petroleum fractions, with the aim ofconverting them into lighter fractions, that are easier to transport ortreat using the usual refining processes. Oils from coal hydrogenationcan also be treated. In this case, it is preferable to use ebullated bedreactors.

[0076] More particularly, the invention solves the problem oftransforming a non transportable viscous heavy oil, which is rich inmetals and sulphur, and contains more than 50% of constituents with anormal boiling point of more than 520° C. to a stablehydrocarbon-containing product which can easily be transported, andhaving a reduced metals and asphaltenes content and a reduced content,for example less than 20% by weight, of constituents with a normalboiling point of more than 520° C.

[0077] In a particular implementation, before sending the feed to theguard reactors, it is first mixed with hydrogen and subjected tohydrovisbreaking conditions.

[0078] In a further implementation, the atmospheric residue or vacuumresidue can undergo deasphalting using a solvent, for example ahydrocarbon-containing solvent or a solvent mixture. The most frequentlyused hydrocarbon-containing solvent is a paraffinic, olefinic oralicyclic hydrocarbon (or hydrocarbon mixture) containing 3 to 7 carbonatoms. This treatment is generally carried out under conditions that canproduce a deasphalted product containing less than 0.05% by weight ofasphaltenes precipitated by heptane in accordance with the AFNOR NF T60115 standard. This deasphalting can be carried out using the proceduredescribed in the Applicant's patent U.S. Pat. No. 4,715,946. Thesolvent/feed volume ratio will usually be about 3:1 to about 4:1 and theelementary physico-chemical operations which are comprised in theoverall deasphalting operation (mixing-precipitation, decanting theasphaltene phase, washing-precipitation of the asphaltene phase) willusually be carried out separately. The deasphalted product is thennormally at least partially recycled to the inlet to the firstfunctioning guard zone.

[0079] Normally the solvent for washing the asphaltene phase is the sameas that used for precipitation.

[0080] The mixture between the feed to be deasphalted and deasphaltingsolvent is usually carried out upstream of the exchanger which adjuststhe temperature of the mixture to a value required to carry out properprecipitation and good decantation.

[0081] The feed-solvent mixture preferably passes into the tubes of theexchanger and not on the shell side.

[0082] The residence time of the feed-solvent mixture in the mixtureprecipitation zone is generally about 5 seconds (s) to about 5 minutes(min), preferably about 20 s to about 2 min.

[0083] The residence time for the mixture in the decanting zone isnormally about 4 min to about 20 min.

[0084] The residence time for the mixture in the washing zone generallyremains between about 4 min and about 20 min.

[0085] The rate of rise of the mixtures both in the decanting zone andin the washing zone are usually less than about 1 centimetre per second(cm/s), preferably less than about 0.5 cm/s.

[0086] The temperature applied in the washing zone is usually less thanthat applied in the decanting zone. The temperature difference betweenthese two zones will normally be about 5° C. to about 50° C.

[0087] The mixture from the washing zone will usually be recycled in thedecanter and advantageously upstream of the exchanger located at theinlet to the decanting zone.

[0088] The solvent/asphaltene ratio recommended in the washing zone isabout 0.5:1 to about 8:1 and preferably about 1:1 to about 5:1.

[0089] Deasphalting can comprise two stages, each stage including thethree elementary phases of precipitation, decanting and washing. In thisprecise case, the temperature recommended in each phase of the firststage is preferably on average less than about 10° C. to about 40° C. atthe temperature of each phase corresponding to the second stage.

[0090] The solvents which are used can also be C1 to C6 alcohols orphenols or glycol type solvents. However, paraffinic and/or olefinicsolvents containing 3 to 6 carbon atoms are highly advantageously used.

[0091] In summary, in one variation, the process of the inventionconsists in a process for hydrotreating, in at least two sections, aheavy hydrocarbon fraction containing sulphur-containing and metallicimpurities, in which in a first, hydrodemetallisation, section, thehydrocarbon feed and hydrogen are passed over a hydrodemetallisationcatalyst under hydrodemetallisation conditions, then the effluent fromthe first stage is passed over a hydrodesulphurisation catalyst in asubsequent second section under hydrodesulphurisation conditions, and inwhich the hydrodemetallisation section comprises one or morehydrodemetallisation zones preceded by at least two hydrodemetallisationguard zones disposed in series for use in a cycle consisting ofsuccessive repetitions of steps b) and c) defined below, thehydrodemetallisation and/or hydrodesulphurisation sections beingcomposed of one or more reactors which can be short-circuited separatelyor otherwise following step d) defined below, said hydrotreatmentprocess comprising:

[0092] a) a step in which the guard zones are used all together for aperiod at most equal to the deactivation time and/or clogging time ofone thereof;

[0093] b) a step during which the deactivated and/or clogged guard zoneis short-circuited and the catalyst it contains is regenerated and/orreplaced by fresh or regenerated catalyst;

[0094] c) a step during which the guard zones are used all together, theguard zone in which the catalyst has been regenerated and/or replacedduring the preceding step being reconnected and said step being carriedout for a period at most equal to the deactivation and/or clogging timeof one of the guard zones;

[0095] d) a step in which at least one of the reactors from thehydrodemetallisation section and/or the hydrodesulphurisation sectioncan be short-circuited during a cycle when the catalyst is deactivatedand/or clogged for regeneration and/or replacement by fresh orregenerated catalyst.

[0096] In a further variation, the process of the invention consists ina process for hydrotreating, in at least two sections, a heavyhydrocarbon fraction containing sulphur-containing and metallicimpurities, in which in a first, hydrodemetallisation, section, thehydrocarbon feed and hydrogen are passed over a hydrodemetallisationcatalyst under hydrodemetallisation conditions, then the effluent fromthe first stage is passed over a hydrodesulphurisation catalyst in asubsequent second section under hydrodesulphurisation conditions, and inwhich the hydrodemetallisation section comprises one or morehydrodemetallisation zones preceded by at least one hydrodemetallisationguard zone, the hydrodemetallisation and/or hydrodesulphurisationsections being composed of one or more reactors which can beshort-circuited separately or otherwise following step d) defined below,said hydrotreatment process comprising:

[0097] a) a step in which the guard zone is used for a period atmost-equal to the deactivation time and/or clogging time of said zone;

[0098] b) a step during which the deactivated and/or clogged guard zoneis short-circuited and the catalyst it contains is regenerated and/orreplaced by fresh or regenerated catalyst;

[0099] c) a step during which the guard zone in which the catalyst hasbeen regenerated and/or replaced during the preceding step isreconnected, said step being carried out for a period at most equal tothe deactivation and/or clogging time of one of the guard zones;

[0100] d) a step in which at least one of the reactors from thehydrodemetallisation section and/or the hydrodesulphurisation sectioncan be short-circuited during a cycle when the catalyst is deactivatedand/or clogged for regeneration and/or replacement by fresh orregenerated catalyst.

[0101] In a further variation, the process of the invention consists ina process for hydrotreating, in at least two sections, a heavyhydrocarbon fraction containing sulphur-containing and metallicimpurities, in which in a first, hydrodemetallisation, section, thehydrocarbon feed and hydrogen are passed over a hydrodemetallisationcatalyst under hydrodemetallisation conditions, then the effluent fromthe first section is passed over a hydrodesulphurisation catalyst in asubsequent second section under hydrodesulphurisation conditions, and inwhich the hydrodemetallisation section comprises one or morehydrodemetallisation zones preceded by at least two hydrodemetallisationguard zones comprising one or more reactors, preferably fixed bed orebullated bed zones, disposed in series for use in a cycle consisting ofsuccessive repetitions of steps b) and c) defined below, thehydrodemetallisation and/or hydrodesulphurisation sections beingcomposed of one or more reactors which can be short-circuited separatelyor otherwise following step d) defined below, said hydrotreatmentprocess comprising:

[0102] a) a step in which the guard zones are all used together for aperiod at most equal to the deactivation and/or clogging time of theguard zone the most upstream with respect to the overall direction ofcirculation of the treated feed;

[0103] b) a step during which the feed penetrates directly into theguard zone located immediately after that which was the most upstreamduring the preceding step and during which the guard zone which was themost upstream during the preceding step is short-circuited and thecatalyst which it contains is regenerated and/or replaced by freshcatalyst; and

[0104] c) a step during which the guard zones are used all together, theguard zone in which the catalyst has been regenerated and/or replacedduring step b) being reconnected so as to be downstream of the set ofguard zones and said step being continued for a period at most equal tothe deactivation and/or clogging time of the guard zone which duringthis step is the most upstream with respect to the overall direction ofcirculation of the treated feed;

[0105] d) a step in which at least one of the reactors from thehydrodemetallisation section and/or hydrodesulphurisation section can beshort-circuited during the cycle when the catalyst is deactivated and/orclogged to be regenerated and/or replaced by fresh or regeneratedcatalyst.

[0106] Preferably, in the process of the invention, a quantity of middledistillate generally representing 0.5% to 80% by weight with respect tothe weight of hydrocarbon feed is introduced into the inlet to the firstfunctioning guard zone. More preferably, the atmospheric distillateintroduced with the hydrocarbon feed is a straight run gas oil.

[0107] In the process of the invention, the product from thehydrodesulphurisation step is preferably sent to an atmosphericdistillation zone from which an atmospheric distillate is recovered atleast a portion or which is preferably recycled to the inlet to thefirst functioning guard zone, and an atmospheric residue is alsorecovered. More preferably, at least a portion of a gas oil fractionfrom the atmospheric distillation step following:thehydrodesulphurisation step is recycled to the inlet to the firstfunctioning guard zone.

[0108] In a preferred variation of the process of the invention, therecycled gas oil fraction is a cut with an-initial boiling point ofabout 140° C. and an end point of about 400° C.

[0109] In these preferred variations, the quantity of atmosphericdistillate and/or gas oil introduced to the inlet to the firstfunctioning guard zone at the same time as the feed preferablyrepresents about 1% to 50% by weight with respect to the feed.

[0110] It is also possible to send at least a portion of the atmosphericresidue from the atmospheric distillation zone to a vacuum distillationzone from which a vacuum distillate is recovered, at least a portion ofwhich is recycled to the inlet to the first functioning guard zone, anda vacuum residue is also recovered. In this case, in a preferredvariation, at least a portion of the atmospheric residue and/or vacuumdistillate is sent to a catalytic cracking unit from which an LCOfraction and an HCO fraction are recovered, and at least a portion ofone or the other or a mixture of the two fractions is sent to the inletto the first functioning guard zone.

[0111] In a preferred mode of the process of the invention, during stepc), the guard zones are used all together, the guard zone in which thecatalyst has been regenerated during step b) being reconnected such thatthe connection is identical to that it had before it was short-circuitedduring step b).

[0112] In a further preferred mode of the process of the invention, aconditioning section is associated with the guard zone or zones, whichsection enables short-circuiting or permutation of said guard zone orzones during operation, without the unit ceasing operation, said sectionbeing regulated so as to condition the catalyst contained in the guardzone which is not functioning, at a pressure in the range 1 MPa to 5MPa.

[0113] In a preferred mode of the process of the invention, in order totreat a feed constituted by a heavy oil or a heavy oil fractioncontaining asphaltenes, the feed is initially subjected tohydrovisbreaking conditions, mixed with hydrogen, before sending thefeed to the guard zone or zones.

[0114] In a preferred mode of the process of the invention, theatmospheric residue obtained from the optional atmospheric distillationstep undergoes deasphalting using a solvent or a solvent mixture and atleast a portion of the deasphalted product is recycled to the inlet tothe first functioning guard zone.

[0115] In a preferred mode of the process of the invention, the vacuumresidue obtained from the optional vacuum distillation step undergoesdeasphalting using a solvent or solvent mixture and at least a portionof the deasphalted product is recycled to the inlet to the firstfunctioning guard zone.

[0116] In a further preferred variation of the process of the invention,all of the reactors are fixed bed reactors. In a further preferredvariation, at least one of the guard reactors and/orhydrodemetallisation sections and/or hydrodesulphurisation sections isan ebullated bed reactor. In a further preferred variation, the reactorsfor the guard zones are fixed bed reactors, and all of the reactors inthe hydrodesulphurisation zone are ebullated bed reactors.

[0117] In a yet still further preferred variation, all of the reactorsin the guard zone are fixed bed reactors, and all the reactors in thehydrodemetallisation zone are ebullated bed reactors, and optionally andhighly preferably, all of the hydrodesulphurisation zone reactors arealso ebullated bed reactors. It is also possible to operate the processof the invention with only ebullated bed reactors in the guard zones andin the hydrodemetallisation and hydrodesulphurisation sections.

[0118]FIG. 1 briefly illustrates the invention.

[0119] The feed arrives in guard zones 1A and 1B via line 1 and leavesthese zones via line 13, line 23 and/or line 24. The feed leaving theguard zone or zones arrives via line 13 in the HDM section which isshown here by a reaction section 2 constituted by one or morereactor(s), each reactor being provided with its own short-circuit. Theeffluent from section 2 is withdrawn via line 14 then sent to ahydrodesulphurisation section 3 which can comprise one or more reactorsthat may be in series, and my optionally be provided with their ownshort-circuit. The effluent from section 3 is withdrawn via line 15.

[0120] In the illustration of FIG. 1, a middle distillate is introducedvia line 55 and is mixed with the hydrocarbon feed in line 1.

[0121] In the case shown in FIG. 1, the guard zone comprises 2 reactors;in its preferred implementation, the process will comprise a series ofcycles each comprising four successive periods:

[0122] a first period during which the feed successively traverses zone1A then zone 1B and in which the gas oil fraction from atmosphericdistillation which is recycled is introduced with the feed into zone 1A;during the first period [step a) of the process], the feed is introducedvia line 1 and line 21 comprising a valve 31 open towards the guardreactor 1A. During this period, valves 32, 33 and 35 are closed. Theeffluent from zone 1A is sent via a line 23, line 26, comprising an openvalve 34 and line 22 to guard reactor 1B. The effluent from zone 1B issent via line 24, comprising an open valve 36, and line 13, whichcomprises an open valve 37, to HDM section 2.

[0123] a second period during which the feed traverses only zone 1B andin which the gas oil fraction from atmospheric distillation which isrecycled is introduced with the feed into zone 1B. During the secondperiod [step b) of the process], valves 31, 33, 34 and 35 are closed andthe feed is introduced via line 1 and line 22, comprising an open valve32, into zone 1B. During this period the effluent from zone 1B is sentvia line 24 comprising an open valve 36 and line 13, which comprises anopen valve 37 to HDM section 2;

[0124] a third period during which the feed successively traverses zone1B then zone 1A and in which the gas oil fraction from atmosphericdistillation which is recycled is introduced into zone 1B with the feed.During the third period [step c) of the process], valves 31, 34 and 36are closed and valves 32, 33 and 35 are open. The feed is introduced vialine 1 and line 22 into zone 1B. The effluent from zone 1B is sent vialine 24, line 27 and line 21 to guard reactor 1A. The effluent from zone1A is sent via line 23 and line 13, which comprises an open valve 37, toHDM section 2;

[0125] a fourth period during which the feed only traverses guard zone1A and in which the gas oil fraction from atmospheric distillation whichis recycled is introduced into zone 1A with the feed.

[0126] The number of cycles carried out for the guard reactors is afunction of the duration of the operating cycle of the whole unit andthe average frequency of permutation of zones 1A and 1B. During thefourth period, valves 32, 33, 34 and 36 are closed and valves 31 and 35are open. The feed is introduced into zone 1A via line 1 and line 21.During this period, the effluent from zone 1A is sent to HDM section 2via line 23 and line 13 which comprises an open valve 37.

[0127] In the case shown in FIG. 1, hydrodemetallisation (HDM) section 2can comprise one or more reactors. Each or a plurality of these reactorscan be temporarily isolated for periodic renewal of the catalyst(s)[step d) of the process]. In its preferred implementation, the processcomprises a series of cycles each comprising three successive periods:

[0128] a first period during which the feed successively traverses guardzones 1A, 1B and HDM section 2, then finally HDS section 3. During thisperiod, the gas oil fraction from atmospheric distillation which isrecycled is introduced into guard zone 1A with the feed. During thisperiod, valves 32, 33, 35, 38 and 41 are closed. The feed is introducedinto zone 1A via line 1 and line 21. The effluent from zone 1A is sentto guard zone 1B via a line 23, line 26, comprising an open valve 34 andline 22. The effluent from zone 1B is sent to HDM section 2 via line 24,comprising an open valve 36, and line 13, which comprises an open valve37. The effluent from section 2 is sent to HDS section 3 via line 14which comprises two open valves 42 and 39. The effluent from section 3is then sent to a fractionation unit (not shown) via line 15 whichcomprises an open valve 40.

[0129] a second period during which the feed successively traversesguard zones 1A and 1B, then HDS section 3. During this period, the gasoil fraction from atmospheric distillation which is recycled isintroduced into zone 1B with the feed. During this operation, valves 32,33, 35, 37, 41 and 42 are closed. The feed is introduced into zone 1Avia line 1 and line 21. The effluent from zone 1A is sent to guard zone1B via line 23, line 26 which comprises an open valve 34, and line 22.The effluent from zone 1B is sent to HDS section 3 via line 24, whichcomprises an open valve 36, and line 25 which comprises two open valves38 and 39. The effluent from section 3 is then sent to fractionationunit (not shown), via line 15, which comprises an open valve 40. Duringthis period, the HDM catalyst is renewed, then said catalyst isconditioned using the method described in this invention. Thisconditioning is particularly necessary if the catalyst is in the oxideform;

[0130] a third period during which the feed successively traverses guardzones 1A and 1B, and HDM section 2, then HDS section 3. During thisperiod, the gas oil fraction from the atmospheric distillation stepwhich is recycled is introduced with the feed into guard zone 1B. Thissituation is identical to the first period and allows the reactorcontaining the fresh catalyst to be replaced in an identical position,in the fluid circuit, compared with that described in the first period.

[0131] In the case represented in FIG. 1, hydrodesulphurisation section3 can comprise one or more reactors; each or a plurality of thesereactors can be temporarily isolated to renew the catalyst periodically[step d) of the process]. In its preferred implementation, the processcomprises a series of cycles each comprising three successive periods:

[0132] a first period during which the feed successively traverses guardzones 1A, 1B and HDM section 2, then HDS section 3. During this period,the gas oil fraction from atmospheric distillation which is recycled isintroduced with the feed into guard zone 1A. During this period, valves32, 33, 35, 38 and 41 are closed. The feed is introduced into guard zone1A via line 1 and line 21. The effluent from guard zone 1A is sent toguard zone 1B via line 23, line 26, comprising an open valve 34 and line22. The effluent from guard zone 1B is sent to HDM section 2 via line24, comprising an open valve 36, and line 13, which comprises an openvalve 37. The effluent from section 2 is sent to section 3 via line 14which comprises two open valves 42 and 39. The effluent from section 3is then sent to a fractionation unit (not shown) via line 15 whichcomprises an open valve 40.

[0133] a second period during which the feed successively traversesguard zones 1A and 1B, then HDM section 2. During this period, the gasoil fraction from atmospheric distillation which is recycled isintroduced with the feed into zone 1B. During this operation, valves 32,33, 35, 38, 39 and 40 are closed. The feed is introduced into zone 1Avia line 1 and line 21. The effluent from zone 1A is sent to zone 1B vialine 23, line 26 which comprises an open valve 34, and line 22. Theeffluent from zone 1B is sent to HDM section 2 via line 24, whichcomprises an open valve 36, and line 13 which comprises an open valve37. The effluent from section 2 is then sent to fractionation unit (notshown), via line 14, which comprises an open valve 42, and line 16,which comprises an open valve 41. During this period, the catalyst orcatalysts from section 3 are renewed, then said catalyst or catalystsare conditioned using the method described in this invention. Thisconditioning is particularly necessary when the catalyst is in the oxideform;

[0134] a third period during which the feed successively traverses guardzones 1A and 1B, and HDM section 2, then HDS section 3. During thisperiod, the gas oil fraction from the atmospheric distillation stepwhich is recycled is introduced into zone 1B with the feed. Thissituation is identical to that described in period 1 and allows thereactor containing the fresh catalyst(s) to be replaced in the sameposition, in the fluid circuit, as that described in the first period.

1. A process for hydrotreating, in at least two sections, a heavyhydrocarbon fraction containing sulphur-containing and metallicimpurities, in which, in a first hydrodemetallisation section, thehydrocarbon feed and hydrogen are passed over a hydrodemetallisationcatalyst under hydrodemetallisation conditions, then the effluent fromthe first stage is passed over a hydrodesulphurisation catalyst in asubsequent second section under hydrodesulphurisation conditions, and inwhich the hydrodemetallisation section comprises one or morehydrodemetallisation zones preceded by at least two hydrodemetallisationguard zones disposed in series for use in cycles consisting ofsuccessive repetitions of steps b) and c) defined below, thehydrodemetallisation and/or hydrodesulphurisation sections beingcomposed of one or more reactors which can be short-circuited separatelyor otherwise following step d) defined below, said hydrotreatmentprocess comprising: a) a step in which the guard zones are used alltogether for a period at most equal to the deactivation time and/orclogging time of one thereof; b) a step during which the deactivatedand/or clogged guard zone is short-circuited and the catalyst itcontains is regenerated and/or replaced by fresh-or regeneratedcatalyst; c) a step during which the guard zones are used all together,the guard zone in which the catalyst has been regenerated and/orreplaced during the preceding step being reconnected and said step beingcarried out for a period at most equal to the deactivation and/orclogging time of one of the guard zones; d) a step in which at least oneof the reactors from the hydrodemetallisation section and/or thehydrodesulphurisation section can be short-circuited during a cycle whenthe catalyst is deactivated and/or clogged for regeneration and/orreplacement by fresh or regenerated catalyst.
 2. A process forhydrotreating, in at least two sections, a heavy hydrocarbon fractioncontaining sulphur-containing and metallic impurities, in which, in afirst hydrodemetallisation section, the hydrocarbon feed and hydrogenare passed over a hydrodemetallisation catalyst underhydrodemetallisation conditions, then the effluent from the first stageis passed over a hydrodesulphurisation catalyst in a subsequent secondsection under hydrodesulphurisation conditions, and in which thehydrodemetallisation section comprises one or more hydrodemetallisationzones preceded by at least one guard zone, the hydrodemetallisationand/or hydrodesulphurisation sections being composed of one or morereactors which can be short-circuited separately or otherwise followingstep d) defined below, said hydrotreatment process comprising: a) a stepin which the guard zone is used for a period at most equal to thedeactivation time and/or clogging time of said zone; b) a step duringwhich the deactivated and/or clogged guard zone is short-circuited andthe catalyst it contains is regenerated and/or replaced by fresh orregenerated catalyst; c) a step during which the guard zone in which thecatalyst has been regenerated and/or replaced during the preceding stepis reconnected, said step being carried out for a period at most equalto the deactivation and/or clogging time of one of the guard zones; d) astep in which at least one of the reactors from the hydrodemetallisationsection and/or the hydrodesulphurisation section can be short-circuitedduring a cycle when the catalyst is deactivated and/or clogged forregeneration and/or replacement by fresh or regenerated catalyst.
 3. Aprocess for hydrotreating, in at least two sections, a heavy hydrocarbonfraction containing sulphur-containing and metallic impurities in which,in a first hydrodemetallisation section, the hydrocarbon feed andhydrogen are passed over a hydrodemetallisation catalyst underhydrodemetallisation conditions, then the effluent from the first stageis passed over a hydrodesulphurisation catalyst in a subsequent secondsection under hydrodesulphurisation conditions, and in which thehydrodemetallisation section comprises one or more hydrodemetallisationzones preceded by at least two hydrodemetallisation guard zonescomprising one or more reactors, preferably fixed or ebullated bedreactors, disposed in series for use in cycles consisting of successiverepetitions of steps b) and c) defined below, the hydrodemetallisationand/or hydrodesulphurisation sections being composed of one or morereactors which can be short-circuited separately or otherwise followingstep d) defined below, said hydrotreatment process comprising: a) a stepin which the guard zones are all used together for a period at mostequal to the deactivation and/or clogging time of the guard zone themost upstream with respect to the overall direction of circulation ofthe treated feed; b) a step during which the feed penetrates directlyinto the guard zone located immediately after that which was the mostupstream during the preceding step and during which the guard zone whichwas the most upstream during the preceding step is short-circuited andthe catalyst which it contains is regenerated and/or replaced by freshcatalyst; and c) a step during which the guard zones are used alltogether, the guard zone in which the catalyst has been regeneratedand/or replaced during step b) being reconnected so as to be downstreamof the set of guard zones and said step being continued for a period atmost equal to the deactivation and/or clogging time of the guard zonewhich during this step is the most upstream with respect to the overalldirection of circulation of the treated feed; d) a step in which atleast one of the reactors from the hydrodemetallisation section and/orhydrodesulphurisation section can be short-circuited during the cyclewhen the catalyst is deactivated and/or clogged to be regenerated and/orreplaced by fresh or regenerated catalyst.
 4. A process according to anyone of claims 1 to 3, in which a quantity of middle distillaterepresenting 0.5% to 80% by weight with respect to the weight ofhydrocarbon feed is introduced into the inlet to the first operatingguard zone.
 5. A process according to claim 4, in which the atmosphericdistillate introduced with the hydrocarbon feed is a straight run gasoil.
 6. A process according to any one of claims 1 to 5, in which theproduct from the hydrodesulphurisation step is sent to an atmosphericdistillation zone from which an atmospheric distillate is recovered atleast a portion of which is recycled to the inlet to the firstfunctioning guard zone, and an atmospheric residue is also recovered. 7.A process according to claim 6, in which at least a portion of a gas oilfraction from the atmospheric distillation step following thehydrodesulphurisation step is recycled to the inlet to the firstfunctioning guard zone.
 8. A process according to claim 5 or claim 7, inwhich the recycled gas oil fraction is a cut with an initial boilingpoint of about 140° C. and an end point of about 400° C.
 9. A processaccording to any one of claims 4 to 8, in which the quantity ofatmospheric distillate and/or gas oil introduced to the inlet to thefirst functioning guard zone at the same time as the feed representsabout 1% to 50% by weight with respect to the feed.
 10. A processaccording to claim 6 or claim 7, in which at least a portion of theatmospheric residue from the atmospheric distillation zone is sent to avacuum distillation zone from which a vacuum distillate is recovered, atleast a portion of which is recycled to the inlet to the firstfunctioning guard zone, and a vacuum residue is also recovered.
 11. Aprocess according to claim 10, in which at least a portion of theatmospheric residue and/or vacuum distillate is sent to a catalyticcracking unit from which an LCO fraction and an HCO fraction arerecovered, and at least a portion of one or the other or a mixture ofthe two fractions is sent to the inlet to the first functioning guardzone.
 12. A process according to any one of claims 1 to 3, in whichduring step c), the guard zones are used all together, the guard zone inwhich the catalyst has been regenerated during step b) being reconnectedsuch that the connection is identical to that it had before it wasshort-circuited during step b).
 13. A process according to any one ofclaims 1 to 12, in which a conditioning section is associated with theguard zone or zones, which zone enables short-circuiting or permutationduring operation of said guard zone or zones, without the unit ceasingoperation, said section being regulated so as to condition the catalystcontained in the guard zone which is not functioning, at a pressure inthe range 1 MPa to 5 MPa.
 14. A process according to any one of claims 1to 13, in which, in order to treat a feed constituted by a heavy oil ora heavy oil fraction containing asphaltenes, the feed is initiallysubjected to hydrovisbreaking conditions, mixed with hydrogen, beforesending the feed to the guard zone or zones.
 15. A process according toany one of claims 7, 10 or 11, in which the atmospheric residueundergoes deasphalting using a solvent or a solvent mixture and at leasta portion of the deasphalted product is recycled to the inlet to thefirst functioning guard zone.
 16. A process according to claim 10 orclaim 11, in which the vacuum residue undergoes deasphalting using asolvent or solvent mixture and at least a portion of the deasphaltedproduct is recycled to the inlet to the first functioning guard zone.17. A process according to any one of claims 1 to 16, in which all ofthe reactors are fixed bed reactors.
 18. A process according to any oneof claims 1 to 17, in which at least one of the guard zone and/orhydrodemetallisation section and/or hydrodesulphurisation sectionreactors is an ebullated bed reactor.
 19. A process according to claim18, in which all of the reactors for the guard zones are fixed bedreactors, and all of the reactors in the hydrodesulphurisation zone areebullated bed reactors.
 20. A process according to claim 18 or claim 19,in which all of the reactors in the guard zones are fixed bed reactors,and all the reactors in the hydrodemetallisation zone are ebullated bedreactors.